At the present time, interlocking building blocks of rectangular shape have conical recesses in their lower faces and complemental conical projections on their upper faces. The recesses and projections are ordinarily arranged in similar patterns of two rows with four elements in each row which are all equidistantly spaced apart so that the four recesses and projections at each end define a square and the four central or intermediate recesses and projections define a square of the same size and shape as the end squares.
These building blocks are of a cementitious material and are ordinarily formed in molds which from the view point of efficiency of production casts a plurality of the blocks on a single operation. Such molds include as an essential element, a lower die plate which is formed with a plurality of frusto conical recesses which form projections on the blocks. The recesses in the blocks themselves are formed by apparatus and steps which are not a part of the present invention.
After a block has been cast, an upper mold part is removed and the blocks are subject to subsequent handling. It is the practice to remove the blocks from the upper die plate and cure them on a pallet so that they can be handled in multiple lots. The lower die plates which are now known and available are not shaped and sufficiently strong and rigid to permit them for use as a pallet for this subsequent handling of the blocks.